Measuring Myelin Loss in the Aging Brain
Myelin acts as an insulating sheath for the axonal connections that exist between neurons, and is necessary for the correct function of these connections. Demyelinating diseases such as multiple sclerosis are particularly debilitating due to the spreading and progressively worsening failure of the nervous system caused by loss of myelin. Unfortunately myelin is also lost to a lesser degree with advancing age, one of many consequences of accumulated molecular damage and maladaptive reactions to that damage. Here, researchers report on efforts to better measure the loss of myelin that occurs with age, comparing established with novel approaches to the challenge of measuring specific structural aspects of the living brain via imaging technologies.
The study of myelination in the brain is essential due to its profound impact on neural function. Myelin acts as an insulator, significantly increasing the speed and efficiency of electrical signal transmission within the nervous system, facilitating information processing and precise neuron communication. Myelination is crucial during early development and continues to influence learning, memory, and cognitive function throughout life.
Recent studies showed that the myelin of the brain changes in the life span, and demyelination contributes to the loss of brain plasticity during normal aging. Diffusion-weighted magnetic resonance imaging (dMRI) allows studying brain connectivity in vivo by mapping axons in white matter with tractography algorithms. However, dMRI does not provide insight into myelin; thus, combining tractography with myelin-sensitive maps is necessary to investigate myelin-weighted brain connectivity. Tractometry is designated for this purpose, but it suffers from some serious limitations. Our study assessed the effectiveness of the recently proposed Myelin Streamlines Decomposition (MySD) method in estimating myelin-weighted connectomes and its capacity to detect changes in myelin network architecture during the process of normal aging. This approach opens up new possibilities compared to traditional Tractometry.
Our results show that the changes occurring in myelin network architecture due to aging have critical effects on network connection strength and efficiency. Specifically, we found that efficiency and mean strength extracted from myelin-weighted connectomes reach their highest point of development around 40 years of age; after this peak, the natural degeneration of axonal microstructure begins. In the broader context of our study, which explores the overall architecture of the myelin-weighted connectome, MySD outperforms traditional Tractometry-based approaches in detecting myelin network changes during normal aging.